{  ACMP.RU
   Problem 2. Text of problem: http://acmp.ru/?main=task&id_task=2
   Verdict: Accepted
}

var n,i:longint; res:int64;
begin
reset(input,'input.txt');
rewrite(output,'output.txt');
readln(n);
res:=0;
if n<1 then begin
	for i:=1 downto n do inc(res,i);
end else begin
	for i:=1 to n do inc(res,i);
end;
writeln(res);
end.